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'J                         226                             Eccentric Rods.

As with No. IL, these are first centred, and. scribed on the flat
cheeks (D); then turned and screwed, and shaped on the cheeks.
The hole is next struck as at E, drilled, and the outer curve milled ;
and the fork (F) is taken out last by drilling and slotting. Broach
right through, and turn the pin as was described for No. III.

The Nuts are best finished by putting a number of them
after  drilling  to tapping size, upon a  mandrel, which is then
placed between dividing centres on a milling machine, and milled
}                            by means of twin mills (see B).    They are to be turned axially

:                        through 6*0° at each operation, and must be afterwards tapped,

1                         and chucked in the lathe for facing and chamfering.

ij                                  X. Expansion Eccentric Rod (Fig. 240).—Centre this;

'I                           also mark the length between the shoulders, and square up the

thickness of the T end.    Turn to the requisite taper by * setting
over5 the loose headstock, as shewn in plan at J,  so that the
j                            front surface of the rod will then be parallel with the lathe bed.

The amount of set-over will, of course, be equal to half the
difference of the two end diameters.    Surface also the T" end.
Remove from the lathe, lay level as at K, and scribe the cheeks b.
(''                           Square and scribe the tee at a to dimensions, measuring from

\\ '                          centre, and strike also the bolt-holes.    Drill these to clearance

\ !                        size, and shape a and b.    Then mark out the eye as at L and

i                         mill this with a cutter having the proper curvatures.    The rod is

;                            long, but as the milling only requires it to sweep through a semi-

* «                          circle, there will be no serious difficulty if it be well clamped.

> .;                              XI. Main Eccentric Rod (Fig. 241) presents no difficulty

\   ',                       after the previous descriptions.   (See Appendix //.,/. 818.)

C                               XII.   Intermediate Valve Rod (Fig. 242).—-This also

%                            would be tooled by previous methods.    The manner of fastening

ij                            the pin is worthy of notice.    The bearing surfaces of the fork are

|                            but narrow, and it is unwise to allow movement at that place;

the die, on the contrary, has a good wide surface, so it is there
only that wear should  be allowed.    After the pin is put in
position, a parallel hole is drilled right through the fork, and
|   !                         enlarged with taper rimer, the pin for this hole being turned in

the lathe with an oblique hand feed. All them pins are of steel]
and all wearing surfaces are cast-hardened.

The Die is surfaced and bored in the lathe, and after wards